The present invention generally relates to storage units, and more particularly to a storage unit which reproduces servo information from medium such as a disk and carries out a servo process for positioning a head.
Portable personal computers such as lap-top computers have become popular, and disk units such as magnetic disk units are often used as storage units of the computers. As a result, the load on the disk unit is increasing every year. The processing speed of a host unit such as the personal computer depends on the data read/write speed of the disk unit which is used as the storage unit, and for this reason, there are demands to further increase the data read/write speed of the disk unit.
In a conventional magnetic disk unit, the positioning of a magnetic head with respect to a magnetic disk based on the servo information reproduced from the magnetic disk by the magnetic head is carried out as shown in FIG. 1, for example. In FIG. 1, a sampling time Ts is made up of a first time Ts1 in which a servo process is carried out for positioning the magnetic head with respect to the magnetic disk, and a second time Ts2 in which a process is carried out with respect to a command request from a host unit such as a personal computer. The servo process is carried out by generating an interrupt with respect to a firmware of the host unit at predetermined intervals. When the servo process ends, the process with respect to the command request is carried out if the command request is received from the host unit.
The first time Ts1 occupies approximately 40% to 50% of the sampling time Ts, and the servo process is carried out constantly because the servo process also has the role of monitoring vibration and shock applied to the magnetic disk unit. On the other hand, it is impossible to know when the command request will be issued from the host unit, and the process with respect to the command request from the host unit is carried out at an arbitrary time during the sampling time Ts.
However, when the command request from the host unit is issued at the start of the sampling time Ts, there was a problem in that the process with respect to this, command request must wait for a time amounting to approximately 40% to 50% of the sampling time Ts. In addition, since the first time Ts1 which is allocated for the servo process occupies. approximately 40% to 50% of the entire sampling time Ts, there was another problem in that the second time Ts2 allocated for the process with respect to the command request cannot be set long.